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What Happens to the Protein You Eat?
Some Review of What are Proteins…? From yesterday
Name the 5 parts of an amino acid, can you draw them?
Central carbon, its “off-side” hydrogen, carboxylic acid group, amine group & side chain (R-group)
What are the 9 AA’s called that the body cannot make? Essential amino acids
What has happened to the protein shown in figure?
The protein has been unfolded or its shape has been changed=
denatured…due to heat, acid, agitation…
Something New!!!
*Conditionally essential amino acids
 Under certain conditions, some nonessential amino acids cannot be made
in body
What Happens to the Protein You Eat?
Notes from animations The Building Blocks of Proteins, Protein Digestion & Protein
Absorption…Watch, listen and if there is something new you wish to recall make a note…
I.
Dietary proteins are digested and absorbed in the stomach and small intestine
a.
Stomach acid (HCl) denatures protein strands and activates __pepsin___.
b. Pepsin form smaller peptides and some amino acids that can move to the SI.
Nutrition & the Human Body – Ch 6 Proteins & Amino Acids
What Happens to the Protein You Eat?
c. Proteases continue the ___digestion ____ in the SI breaking the shorter polypeptides
into tripeptides, dipeptides and amino acids (protein remnants) that are absorbed by
the lining of the SI
d. Protein remnants are broken into single amino acids, are then absorbed into the blood
stream through _____active______ transport (energy requiring movement), and travel
to the liver.
e. How the liver uses these amino acids depends on the needs of your body.
II.
The body degrades and synthesizes proteins.
a.
Blood and cells contain a small supply of amino acid that constantly changes as the
body degrades and synthesizes protein. A limited supply is stored in amino acid pools in
blood and cells for needed protein synthesis
b. The process of continually degrading and synthesizing protein is called protein
___turnover______.
c. AA’s will be broken down when a surplus supply exists.
1.
Carbon containing remnants can be converted to glucose, used as energy, or stored
as ___fat___.
2. Nitrogen in the amine group can be converted to _urea_ and excreted in urine via
the kidneys.
Nutrition & the Human Body – Ch 6 Proteins & Amino Acids
What Happens to the Protein You Eat?
3. Amino acids can be used to make body proteins and non-protein substances
Examples: thyroid hormone, melanin
III.
DNA directs protein synthesis
a.
Each cell contains DNA for making every protein in the body, but each cell does not
make them all.
b. __Genes___ (not the kind you wear): DNA segment that codes for specific protein
1.
c.
DNA provides only the instructions for building and synthesizing
DNA directs RNA to carry out its instructions for building a protein.
1.
There are two specialized RNAs called messenger RNA (mRNA) and transfer RNA
(tRNA).
Nutrition & the Human Body – Ch 6 Proteins & Amino Acids
What Happens to the Protein You Eat?
d.
When abnormalities occur during protein synthesis, serious medical conditions may
result.
1.
Sickle-cell anemia is one potential serious medical condition caused by a change in
the amino acid sequence in the hemoglobin molecule.
2. Phenylketonuria (_PKU_) can cause a buildup of an amino acid in the blood, which
can lead to mental retardation.
The Take-Home Message
With the help of gastric juices and enzymes in your stomach and small intestine, proteins are
broken down into amino acids and absorbed into your blood to be used by your cells. A
limited supply of amino acids exist in pools in your body, which act as reservoir for the
synthesis of protein as needed. Surplus amino acids are broken down, and the carboncontaining remains can be used for glucose or energy, or can be stored as fat, depending on
your body’s needs. The nitrogen excreted in the amine groups is eventually converted to the
waste product urea and is excreted in your urine. Amino acids can be used to create
nonprotein substances, including certain hormones. The synthesis of proteins is directed in
the cell nucleus by DNA, which carries the code for the amino acid sequences necessary to
build the proteins that your need.
Nutrition & the Human Body – Ch 6 Proteins & Amino Acids